Multiple-quantum NMR spectra of partially oriented indene: a new approach to estimating order in a nematic phase

Cyclic J cross polarisation (CYCLCROP) is a sensitive method for the noninvasive monitoring of (13)C distributions and fluxes. The PRAWN rotating frame Hartmann-Hahn mixing sequence ameliorates problems associated with sensitivity to Hartmann-Hahn mismatch and reduces RF power deposition. The combination of CYCLCROP with echo planar imaging (EPI) for spatial encoding of the proton detected carbon signal allows efficient use of the available signal to be made, permitting a significant improvement in the temporal resolution of any study. We report here on some initial experiments to demonstrate the feasibility of echo planar proton detected (13)C imaging using CYCLCROP based upon the PRAWN module, including the application of the technique to the measurement of transport and accumulation of (13)C-labelled sucrose in a castor bean seedling. Two methods that can be used to eliminate the effect of the J-splitting in the EP images are presented. In addition, a fast, image-based B(1) field-mapping method which may be used to quantitatively map the low frequency RF field in a dual resonant ((13)C/(1)H) probe is presented. The technique utilises the above described imaging method, permitting fully quantitative, 64x64 axial field maps to be generated in about a minute.     

Generating sets for compact semisimple Lie groups

Let be a compact connected semisimple Lie group. We prove that the subset of consisting of pairs which topologically generate is Zariski open.

     

Band crossing in 162Dy: Characterisation of negative-parity yrast and yrare sequences

The crossing of an octupole band by a rotation-aligned two-quasiparticle band has been observed in detail in ¹⁶²Dy. Both the yrast and yrare states are identified from the band heads (I =2 and I = 5) to high spin (I ～ 14), with band crossing in both the even-spin and odd-spin sequences.     

An Example of the Application of a Systematic Method to Design

This paper is concerned with using the digital computer as an aid to the solution of a class of multivariable design problems and reports some experience. The input to the computer is a set of design variables and a set of interactions between these variables, while the output consists of a hierarchy of groups of highly interacting variables. Both the preparation of the input and the interpretation of the output depend on subjective decisions by the designer using the computer. A specific application was therefore investigated in which different sets of inputs were compiled by three different designers, using 18, 38, 58 and 185 variables. The four outputs were analysed to compare their usefulness as a design aid in proportion to the effort required for their preparation. An IBM 7044 computer was used and a guide is given for the estimation of program running times on this machine.     

The stereochemistry of cyclisation of n-t-butyldihydrocinnamamide to a β-lactam

Using a stereospecifically labelled precursor, the peroxide catalysed cyclisation of N-$\text{t}$-butyldihydrocinnamamide to the corresponding β-lactam was shown to proceed with complete loss of stereochemistry at the benzylic carbon atom.     

Ab initio and semiempirical estimates of PN valence state interactions

Hartree-Fock wavefunctions for the valence states of PN arising from the lowest energy open shell configurations, 2π⁴7σ3π and 2π³7σ²3π, are generated and used in ab initio calculations of diagonal spin-orbit, off-diagonal spin-orbit, and rotation-electronic matrix elements. These results are compared with those from two semiempirical methods, one based on atomic orbital populations and the other dependent solely on atomic spin-orbit splittings. The latter method is found to be surprisingly successful in predicting the ³Δ spin-orbit constant for a series of isovalent molecules. Semiempirical estimates of the ³Δ and ³Π spin-orbit constants of AsN are given. The Hartree-Fock values of the a and b perturbation parameters are found to be 50 cm⁻¹ and 0.60 (unitless), respectively. A previously reported perturbation in the A¹Π-X¹Σ⁺ band system is shown to arise from a ³Σ^{− 1}Π spin-orbit interaction.     

Critical field for complete vortex expulsion from narrow superconducting strips

We have measured the maximum field for which vortices are completely expelled from a thin-film superconducting strip. Niobium strips of width W were field cooled and imaged with a scanning Hall-probe microscope. Below a critical field B(m) approximately Phi(0)/W(2) all flux was expelled; above this field vortices were observed with a density increasing approximately linearly with field. The small value of the critical field, which is orders of magnitude less than in the bulk, implies that superconducting devices should be designed with narrow wires to eliminate the generation of noise from vortex motion.     

Flexible enzymatic and chemo-enzymatic approaches to a broad range of uridine-diphospho-sugars

Enzymatic and chemo-enzymatic approaches provide straightforward access to uridine diphospho sugars irrespective of the relative and absolute configuration of the sugar, its ring size and substitution pattern.     

Reaction and scattering in cold electron collisions

Experimental data are presented for the scattering of electrons by CCl4 between 8 and 200 meV impact energy. These results are used in conjunction with data for the reactive process, yielding Cl-, to study the low energy behavior of a system which simultaneously displays both reactive and elastic scattering channels. Phase shifts are derived and illustrate how channel competition develops as the energy falls. This behavior and the involvement of vibronic effects at impact energies above approximately 30 meV pose a challenge to theory.